The invention relates to vapor compression systems with enhanced dehumidification capability and, more particularly, to operation of such vapor compression systems to provide dehumidification at low ambient conditions and improvement of such operation.
Operation of vapor compression systems to provide a dehumidification function of an indoor space along with minimum sensible cooling is sometimes necessary. This function is provided utilizing three main design approaches, each of which employs main refrigerant flow, or a portion thereof, for reheat of the dehumidified and overcooled air stream.
The first concept uses compressor discharge gas re-routed to a reheat coil of the system which is placed in the indoor section behind the evaporator and connected sequentially with the main condenser. This allows reheat of the indoor air stream to reduce sensible capacity, after the air stream has been cooled to provide the desired dehumidification.
A second concept also employs compressor discharge gas in a similar fashion with the exception that the reheat coil is placed in parallel arrangement with the main condenser, and the main condenser is taken out of the circuit in the dehumidification mode of operation.
A third approach uses a portion of the compressor discharge gas which is bypassed around the main condenser coil and mixed with the main flow routed through the condenser coil, as usual. The combined flow is then directed through the reheat coil, located behind the evaporator coil, for the reheat function of indoor air stream.
At low ambient conditions, the foregoing methods can result in undesirable two-phase flow at the inlet of the expansion device of the system as well as evaporator freeze-up. Furthermore, when operating at low compression ratios, system dehumidification efficiency can suffer in terms of lost latent capacity, increased sensible capacity, reduction in supply air temperature and drop of the system latent efficiency.
It is clear that the need remains for an improved method for operating a vapor compression system for providing dehumidification at low ambient conditions.
It is therefore the primary object of the present invention to provide such a method.
It is a further object of the present invention to provide a method for operating a vapor compression system wherein dehumidification is provided with enhanced system efficiency even at low ambient conditions.
Other objects and advantages of the present invention will appear hereinbelow.